Abstract

The AAPG Ad Hoc Committee on Global Climate Issues has studied the supposition of human-induced climate change since the committee's inception in January 1998. This paper details the progress and findings of the committee through June 1999. At that time there had been essentially no geologic input into the global climate change debate. The following statements reflect the current state of climate knowledge from the geologic perspective as interpreted by the majority of the committee membership. The committee recognizes that new data could change its conclusions. The earth's climate is constantly changing owing to natural variability in earth processes. Natural climate variability over recent geological time is greater than reasonable estimates of potential human-induced greenhouse gas changes. Because no tool is available to test the supposition of human-induced climate change and the range of natural variability is so great, there is no discernible human influence on global climate at this time.

Dr. Lee C. Gerhard is currently principal geologyist of the Kansas Geological Survey. His career has included petroleum exploration, reservoir geology, and research management. His research has been dominated by carbonate studies, petroleum occurence, and environment and resources public policy. Prior to returning to Kansas, he was Getty Professor of Geological Engineering at the Colorado School of Mines and operated an independent petroleum exploration company. Lee is an Honory Member of the AAPG.

Introduction

The AAPG Ad Hoc Committee on Global Climate Issues was established by President Edward David in January 1998. The committee was assigned a large task:

"The committee is charged with providing to the Executive Committee and the AAPG members, a scientific foundation for the analysis of geologic data to enlighten the debate on possible causes of ongoing climate change. The committee will also use Earth history to illuminate the possible societal effects of those changes, which can be documented to be occurring. The committee will be responsible for providing the Association with information on the key climate issues facing the energy-related industries. The committee will also gather the existing data that apply to developing an understanding of climate change as it pertains to the energy industry. The sources of information will include not only a summary of key issues and the positions taken by governments, institution, and private interest groups, but by companies within the energy industry itself. It is expected that the committee may offer the AAPG Executive Committee advice and guidance on actions, which the Association might take. Resulting informational materials may be distributed to other committees and to the members in general."

From the beginning it was recognized by the committee that polarized views of climate change already supersede any simplistic treatment of the subject. Political activity assuming anthropogenic climate impacts is so very far out in front of science supporting the supposition that it is very difficult to assess the quality of science presented in the arguments. So little is agreed upon among the scientific community that only a few basic statements can be made. Complicating the setting further, public perception of the issue is one of wonderment and lack of understanding of basic climate information. The public seems to believe that climate is naturally stable and unchanging, much as many believe that the earth is unchanging. It is clear that the geologic perspective on climate change has not been organized and is ignored.

Summary of Committee Work

In this setting, the committee elected to focus its efforts for the year on developing a science-based assessment of the current climate debate, and to sponsor more aggressive scientific research papers dealing with geological constraints on climate. Time, people, or money are not available to develop a full scientific research program for AAPG to address this issue. Federal money has not been made available to support research that is designed to test the supposition of anthropogenic (human-induced) warming.

The committee thus developed its report from study of the literature, using hundreds of hours of volunteer effort. Some of this background has been supplied informally to the Executive Committee. The audience is the AAPG membership, who are knowledgeable scientists about geology, but not climate issues, and AAPG student members and the general public, who may have little background in the sciences necessary to understand the debate. Further, because the committee was charged with presenting information as soon as possible, the committee elected to write its reports in language understood by the lay scientist and referenced sufficiently to get interested readers into the literature on their own.

This paper contains conclusions based on extensive review of the literature plus knowledge of geological processes. Although these are interpretations, most climate science today is interpretive, and there is no short cut to scientific certainty.

We recognize that many readers will appreciate the views of the committee, and some will be distressed to read them. That is the result of violation of the scientific process by politicization before the science is advanced sufficiently to develop consensus as to the possible magnitude of anthropogenic effects (if any) and the impacts on society that could occur.

In that sense, politics are considerably out in front of the supporting science. Although political action has already been proposed and an international treaty has been signed, the science is just now initiating the studies to understand what directs climate changes in magnitude, direction, and rate. Geologists have started developing time and temperature data through recent geologic history to provide other scientists with an accurate assessment of natural variability. We suggest that interested readers may wish to avail themselves of the continuing flow of information and research in the journals Science and Nature. All geologists who are interested in the climate debate probably should read two books, one by Moore and Stott (1996) and the other by Lamb (1995).

As additional activities, at the 1999 Annual Meeting of the AAPG in San Antonio, a forum of scientific papers addressing natural variability was presented, sponsored by the DEG (AAPG's Division of Environ mental Geosciences). Abstracts from that session have been published. One paper from the preliminary report of the 1998 Ad Hoc Committee on Climate Issues is published (Bluemle and Sabel, 1999). Committee members are preparing formal papers on a variety of geologic aspects of climate papers, which may appear as a formal publication or as separate committee reports.

Future Work

The committee is sponsoring a forum at the New Orleans annual meeting in 2000. The format will be invited formal papers, with discussions. We are planning a book publication of these papers and several from the preceding forum. David Jenkins and Douglas Swift were appointed as co-vice-chairs of the committee at the annual meeting in San Antonio. One ultimate goal is the establishment of a consensus geologic time/temperature curve for the last 60 m.y.

Following is the technical work of the committee over the last two years.

An Assessment of Issues

Identifying common ground in the debate has been difficult. The following assessments are highly generalized, and may in themselves be stimuli for debate; however, perhaps we know the following:

Carbon dioxide levels have increased at Mauna Loa, Hawaii, since measurements started in 1958.

There is apparent global warming from the middle of the last century to present. The amount of temperature change is disputed, but is likely to be about 0.5°C.

We also know that the federal government has spent and continues to spend billions of dollars a year on climate studies for assessing the impact of global warming and supporting research into determining the rate of climate warming owing to human-induced carbon dioxide increases. Funding to test the supposition has been much less.

We know that scientists do not fully understand controls on earth climate in the present or in the past.

We know that existing general circulation models are quite imperfect.

We know that geological factors have had little consideration in the international debate over climate change.

We know that the earth's atmosphere and climate are incredibly complex and that simple theoretical models of greenhouse gas/temperature relationships are not adequate to understand present climate changes. Biologic, hydrologic, and solar effects, at least, have significant impacts on climate and complicate any reactions to anthropogenic greenhouse gas concentration changes.

We know that the IPCC (Intergovernmental Panel on Climate Change) considers that the weight of evidence suggests anthropogenic influence on global temperature, but we also know that there is no clear and direct evidence that this is true or false (IPCC, 1998).

We know that natural variability has been debated, but that the geological community has not yet provided the international climate community with a consensus time/temperature curve against which to compare global temperature changes [see Bluemle and Sabel (1999) as a start].

We know that the earth's temperature is rising in some areas and falling in others. We know that systematic measurements of earth surface temperatures have been conducted only for a few years (about 50), and that the corresponding satellite and balloon measurements are not in agreement with surface station measurements. We understand there are heat island effects around cities and other local human-induced climate variations.

We know that statements to the effect that 1998 (or any other modern year) is the hottest year ever are false when placed in context of recorded history.

We know that greenhouse theory posits that increases in any greenhouse gas should directly increase earth temperature. We know modern climate change does not display such direct effects.

But we do not know the following:

We do not know what dynamics control earth temperature and changes in climate.

We do not know how to separate anthropogenic atmospheric changes from natural variability.

We do not know how to account for the sawtooth effect in temperature changes.

We do not know why greenhouse gases abundance varied considerably during pre-human civilization, and how that relates to modern changes.

We do not know how to assess information in the current literature indicating why carbon dioxide across the United States is decreasing, when we are theoretically the largest emitter of the gas (Fan et al., 1998).

There are many other things we do not know. We do not know more than we do know.

Committee Interpretations

With this background, here is a summary of the results of literature study of climate issues developed by the Ad Hoc Committee on Climate Issues. A short bibliography of references related to the statements is provided, but it is not intended to be complete. The committee may develop a more complete recommended reading list in the future.

Methodology of Science and Integrity of Results

Science progresses through observations and experiments designed to test scientific statements and through the development of hypotheses to explain the observations and experiments. Upon continuous testing, some hypotheses appear to be valid, and thus may become theories, but theories are not absolute, and must be continually tested, changed, and refined to encompass all observations and measurements.

Climate change due to greenhouse effects of strictly anthropogenic carbon dioxide is one such supposition. The supposition of human-induced global climate change is currently being hotly debated, with some scientists providing evidence for defense of the supposition and others providing evidence refuting it. This is the nature of science. Thus, it is incumbent upon our community to insist that the supposition be tested against all available observational, experimental, and theoretical means.

Natural greenhouse effects help provide earth with an equable climate; however, it is known that changes in the gaseous composition of the atmosphere could result in a series of very complicated and poorly understood positive and negative feedback because of interactions with the ocean, the lithosphere, and the biosphere. Many scientists challenge the concept and theory that significant global warming is primarily occurring owing to increased industrial revolution carbon dioxide, rather than natural processes that occur over the long term. These challenges provide strong impetus to increased research on climate stability.

New knowledge and improved data increase the likelihood that a substantial and scientifically justified understanding will emerge. New research into solar variability, expanded studies of climate history, ocean role in climate, analysis of the earth's carbon budget, and studies of geological constraints on climate models are just a few of the expanded areas of scientific study that have arisen from this debate. It is imperative that public policy decisions about scientific issues be accompanied by solid science (Sigma Xi, 1994).

The Nature of Geology

Geology is temporal science by its very nature. Geologists view processes and earth history in much longer time increments than most people, which leads us to question conclusions about changes in earth processes and characteristics based on short-time studies. Short-term climate variability deriving from human activities is one such area we are required to question.

Geologists also view the earth as a single dynamic system, whose energy is drawn from the sun and from internal radioactive decay heat. Geologists are well versed about short-term geologic processes, such as volcanism, floods, and earthquakes, but view these in their appropriate time and energy contexts. The immensity of energy levels involved in dynamic earth processes tends to make us discount the effects of humankind on the earth and its natural processes.

The Earth has two heat engines: its own internal radioactive interior with associated fissure and tectonic plate outlets, and the sun. Solar energy arrives in broad-spectrum wavelengths. These heat engines are the only significant earth climate drivers. Ocean currents distribute heat energy around the earth, driving small- and large-scale climate events. Earth tectonics may determine ocean current geometry (Gerhard, 1999).

Geologists also believe the earth is not in dynamic equilibrium. Geologists recognize that change is constant and desirable; an equilibrium earth would be featureless and not very interesting. Dynamic processes continually change the face of the earth. Climate is only one of many processes or characteristics of earth that is never constant. Landscapes change, rocks weather away, and faults change the shape of the earth daily. This is a dynamic earth, and change is constant, even in climate (Moore et al., 1996; Broecker, 1997a, b; Mackenzie, 1998). Climate changes rapidly and irregularly, frequently in a sawtooth pattern.

One of the most fascinating observations now recognized in climate variability is the proclivity of climate to change abruptly, most frequently by rapid warming, followed by slow cooling. This pattern is currently being statistically validated. The phenomenon has been called the "sawtooth effect."

This geometric variation in global temperature occurs at many scales, from multimillennia to less than 50 yr episodes, such as from the mid-1930s to the present. Theories about the origin of this geometry have been advanced, from solar cyclicity to gas hydrate emissions. Lack of correlation between modern carbon dioxide increases and temperature records continue to undermine confidence in the anthropogenic greenhouse supposition of global climate changes. For example, the growth of carbon dioxide in the atmosphere has been rapid from about 1940 to present. The major temperature increase in this century was from about 1932-1938, with cooling from that time forward to the 1980s. There appears to be another warm "sawtooth" jump occurring now, but that is statistically unclear.

Another issue raised by observations of the sawtooth effect is that in ice core data, temperature jumps are not necessarily preceded by greenhouse gas jumps; rather, the elevation of temperature either precedes elevation of greenhouse gas concentration or is roughly coincident with such increases. It is not possible to identify greenhouse gas concentration increases as the driver for temperature from these data. Henry's Law does require increases in atmospheric carbon dioxide from temperature increases in ocean waters. The conclusion that greenhouse gas concentration is derived at least in part from temperature increases can be drawn from the data.

It is clear that additional work is necessary to fully appreciate the relationship between the various greenhouse gases and their impacts on climate, both directly and as feedback mechanisms. Water vapor is difficult to study because of its varying concentrations. Water vapor is the most abundant greenhouse gas, but has extremely complex feedback (Haq, 1998; Stocker, 1998; Davis and Bohling, in press).

The short-term geologic prognosis is for continued natural global warming as temperature warms from the Little Ice Age. The long-term geologic prognosis is a return to ice house conditions.

The Medieval Warm Event (MWE) or Optimum occurred during the period from 1100 to 1300, when many of the castles of Scotland and Sweden were constructed and the Vikings settled agricultural communities on the southern shores of Greenland. Estimates of climate during that warm spell indicate that the global temperature was 1-2°C above our current climate. That rapid warming was followed by slow, but extensive, cooling, such that the Viking colonies died out from starvation during the Little Ice Age (LIA). Plague, pestilence, and starvation haunted Europe, and during our own American Revolution, cold temperatures in Pennsylvania almost devastated the American army at Valley Forge. The generally accepted end of the Little Ice Age is 1850 or later, a five-century-long cooling episode. It was only a few years ago in the 1960s and 1970s that this nation was concerned about global cooling.

Thus, the global climate is just now coming out of the LIA, and a rational prediction is for warming to continue, perhaps to reach MWE levels. Those levels are roughly coincident with the predictions of the Intergovernmental Panel on Climate Change (IPCC) (Houghton et al., 1996) for theoretical anthropogenic greenhouse effect warming. Natural variability encompasses all the best estimates of future anthropogenic warming (Bluemle and Sabel, 1999).

Although we can reasonably predict continued natural warming in the short term, climate history is full of rapid reversals of temperature. Studies of longer term climate suggest that the earth is in a long-term cooling phase, starting about 5000 yr ago. We need to continue to study mitigation of any deleterious effects of continued warming. It is also incumbent upon us to study mitigation and adaptation to long-term cooling, as well as short-term warming. Adaptation to warming may not be technically difficult, but significant cooling could interfere with our ability to feed the world (Frakes, 1979; Grove, 1988; Davis and Bohling, in press; Lamb, 1995; Moore et al., 1996; Bluemle and Sabel, 1999).

Necessary Science Is Yet Undone

Scientific research necessary to understand controls on earth climate is incomplete. New research is addressing many fundamental questions. Some examples are as follows:

Renewed effort in understanding the complexity and intensity of solar variability on earth climate is underway, with some preliminary results indicating episodic or cyclic relationships between earth temperature and solar radiation, especially sunspot cycles. Other longer term cycles appear to have a greater amount of change in solar flux. It is absolutely necessary to comprehend solar energy flux to understand climate (Muller and McDonald, 1997; Raymo, 1998).

A full analysis of the earth's carbon budget has not yet taken place, and new insights or theories abound for why observed carbon dioxide levels do not correspond to the computer model extrapolations. It is not clear that ocean/atmosphere exchanges are fully appreciated. Carbon dioxide concentration in the earth atmosphere is dependent on many other factors besides oxidation of fossil fuels, and carbon dioxide itself is not the primary greenhouse gas (water vapor is). Study of long-term variations in concentration of atmospheric gases is desirable (Fan et al., 1998; Haq, 1998; Kaiser, 1998a, b; Schmidt, 1998).

The role of earth tectonics in climate control is being examined for almost the first time. Rates of weathering and atmospheric gas concentration, ocean circulation changes with tectonics, heat exchange from deep crust to ocean and atmosphere, and other topics are just now being explored. The role of ocean currents in distributing heat from plate boundaries (spreading centers, volcanoes) has not been fully documented (Broecker, 1997a; Ruddiman, 1997; Worm, 1997).

The geologic process, data, and time/temperature history of general circulation models (GCMs) have not been adequately peer reviewed by geologists; consequently, their output is regarded with suspicion by geologists.

No computer model has successfully predictively modeled present climate through the past, extending through the LIA and the MWE. Many initiate at about 1890; a few go as far back as 1500, the time of very deep cold in the LIA. A climate model will have to be developed to successfully predictively model from before the MWE to present (Berkowitz, 1998). Forward modeling, that is, using present parameters to predict climate either in the past or future, is a difficult task even for relatively simple natural systems. The complicated feedback and variable control parameters of full-scale climate forward models become daunting to mathematically replicate.

Although much recent effort has been exerted to analyze natural variability of climate, work remains. A consensus time/temperature curve for the Pleistocene and as much of the Cenozoic as possible is the next step in these studies (Bluemle and Sabel, 1999).

Sea level rise can be generally projected from the 8 ka curve of Adey and Burke (1976). Although it is not really a smooth curve, the rate varies greatly as climate changes rapidly. Isostatic effects must be factored in projections of ultimate sea level elevation, along with thermal expansion of the world ocean. Geological projections are that sea level will rise based on historical climate records; the rate of rise could be affected by human-induced climate changes. Research on mitigation of almost certain natural sea level rise is advised (Adey and Burke, 1976).

There Is Not Now Any Clear Discernible Effect of Human Activities on Global Temperature

Because historical data show that the rate and magnitude of temperature changes caused by factors other than carbon dioxide is very large, it is not possible to demonstrate any clearly discernible discrete evidence of human activities on global temperature.

Climate today is statistically and actually within the natural variable levels experienced by the human population over the last 1000 yr and well within the widely variable levels of the last 10,000 yr. This does not imply that a human effect will not develop, just that there is none clearly apparent in climate data at this time. Our work is to document current and past climate data so as to recognize if such influence takes place.

There are no "flat lines" in climate; global temperatures vary continuously over both short and long time spans, and are never stable. Natural variability greatly exceeds projected human-induced changes. Major cycles of global climate over the last 600 m.y. have been in excess of 8°C, with highly variable levels of carbon dioxide. Data indicate that the earth's climate has been slowly cooling over the last 5000 yr. Within that cooling there are warm periods and colder periods. The climate has been warming since about 1850-1875, coming out of the LIA, with one significant and abrupt episode of warming in the 1930s. That warm episode was followed by 50 yr of gradual cooling. The last few years have been warming again (the sawtooth effect) (Frakes, 1979; Lamb, 1995, Mackenzie, 1998; Bluemle and Sabel, 1999; Davis and Bohling, in press).

Status of Climate Science

It is the opinion of this committee that the science backing substantial political action on anthropogenic carbon dioxide emissions is inadequate and the data, although conflicting, generally do not now demonstrate direct earth temperature linkage to anthropogenic carbon dioxide emission. Sub stantial and high-cost political action on global climate issues is premature until greater knowledge of the climate system is gained.

Funding for research and study of this issue, however, is well advised and necessary to comprehend the complexities of climate and to lay the foundation for whatever action, if any, will be useful in the future. Funding for research should encompass basic understanding of climate, not simply mitigation of assumed deleterious effects of human-induced climate changes. Geologic information and theory suggest that the global climate is likely to continue to warm without regard to any anthropogenic activities, and that considerable research might be useful to adapt to temperatures similar to the MWE.

Long-term indications of global cooling suggest that research into the mitigation of reduced agricultural productivity during an extended cold period would be advisable because the effects of prolonged cold have historically been more severe on all human populations than extended warm. Although this is theoretically a longer term risk, climate has been observed to dramatically change over short periods of time, and this risk cannot be discounted (Fitzpatrick, 1995).

This statement has purposefully not discussed whether climate change may be good, bad, or indifferent to society, nor have we attempted to assess the costs of complying with various proposed treaty obligations to control carbon dioxide concentration growth. The statement is written for scientifically literate but non-climate-specialist readers, and summarizes study of the issues by the committee and committee interpretations of the scientific literature.